linux-kernel - Re: mapcount corruption regression

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Date:   Thu, 3 Dec 2020 06:37:57 +0800
From:   Yi Zhang <yi.zhang@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     "Shutemov, Kirill" <kirill.shutemov@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Toshi Kani <toshi.kani@....com>
Subject: Re: mapcount corruption regression

Hi Dan
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index dfd82f51ba66..7ed99314dcdf 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -829,6 +829,7 @@ int pud_free_pmd_page(pud_t *pud, unsigned long addr)
>          }
>
>          free_page((unsigned long)pmd_sv);
> +       pgtable_pmd_page_dtor(virt_to_page(pmd));
>          free_page((unsigned long)pmd);
>
>          return 1;
>
> In 2013 Kirill noticed that he missed a pmd page table free site:
>
>      c283610e44ec x86, mm: do not leak page->ptl for pmd page tables
>
> In 2018 Toshi added a new pmd page table free site without the destructor:
>
>      28ee90fe6048 x86/mm: implement free pmd/pte page interfaces
>
> In 2020 Willy adds PG_table accounting that flags the missing
> pgtable_pmd_page_dtor()
>
> Yi, I would appreciate a confirmation that the fix works for you.
>
I applied the patch to v5.10-rc3 ~ v5.10-rc6, and cannot reproduce this 
issue with my regression test now, feel free to add:
Tested-by: Yi Zhang <yi.zhang@...hat.com>


Thanks
Yi